Problem 62 - A Complete Resource Book in Chemistry for JEE Main

Question

While moving down a group in the periodic table, which of the following would be true? (1) all the atoms have the same number of valence electrons (2) gram atomic volume increases (3) electronegativity decreases (4) metallic character decreases and the basic nature of their oxides decreases. Select the correct answer by using the following codes: (a) 1,2 and 3 (b) 2,3 and 4 (c) 2 and 3 (d) 1 and 3

Step-by-Step Solution

Answer

The correct answer is (a) 1, 2, and 3.

Step 1: Understand the Periodic Trend

When moving down a group in the periodic table, different trends are observed for various properties such as valence electrons, atomic volume, electronegativity, metallic character, and the nature of oxides. Gathering what occurs to these properties will help us determine the correct statements.

Step 2: Analyze Valence Electrons

In a group, all elements have the same number of valence electrons, meaning that Statement (1) "all the atoms have the same number of valence electrons" is true.

Step 3: Examine Atomic Volume

When moving down a group in the periodic table, the atomic volume generally increases as additional electron shells are added, which increases the atomic radius. Hence, Statement (2) "gram atomic volume increases" is true.

Step 4: Check Electronegativity Trends

Electronegativity decreases down a group because the added electron shells reduce the attraction between the nucleus and the valence electrons. Therefore, Statement (3) "electronegativity decreases" is correct.

Step 5: Consider Metallic Character and Oxide Nature

Metallic character increases down a group as atoms become more willing to lose electrons, and the basic nature of their oxides generally increases. Therefore, Statement (4) "metallic character decreases and the basic nature of their oxides decreases" is false.

Step 6: Identify the Correct Combination

From the analysis, statements (1), (2), and (3) are true, which matches option (a): 1, 2, and 3.

Key Concepts

Valence Electrons

Valence electrons are the electrons located in the outermost shell of an atom. They are incredibly important for determining how an element will react with other substances. Essentially, valence electrons allow elements to bond with each other, forming a range of different compounds.

When you look down a group in the periodic table, each element in that group has the same number of valence electrons. This is why elements within the same group tend to exhibit similar chemical behaviors. For example, all elements in Group 1, known as the alkali metals, have one valence electron, making them highly reactive.

• These electrons are responsible for the properties of the materials.
• They affect the reactivity and bonding behavior of an element.

Knowing the valence electrons helps predict the types of bonds an element can form, which is essential for understanding its role in chemical reactions.

Atomic Volume

Atomic volume refers to the volume that an atom occupies, which is largely determined by the number of electron shells it has. As you move down a group in the periodic table, atomic volume increases. This is because each successive element has an additional electron shell, thus increasing the overall size of the atom.

This increase in atomic volume has several implications:

• Larger atoms with more electron shells naturally have more space between the nucleus and its outer electrons.
• It also affects the density and strength of metallic bonds between atoms.

Understanding atomic volume is crucial because it influences the physical properties of elements, such as melting and boiling points, as well as their reactivity.

Electronegativity

Electronegativity is a measure of how strongly an atom attracts the electrons in a bond. It tells us how much an element wants to "hold onto" its electrons when bonding with other elements. As you move down a group in the periodic table, electronegativity decreases. This decline is generally due to the increasing distance between the nucleus and the valence electrons, caused by the additional electron shells.

This means that elements lower down a group are less greedy for electrons compared to those at the top.

• This trend influences the types of compounds that elements can form.
• Lower electronegativity can often result in more ionic or metallic bonds.

Knowing the electronegativity helps predict the nature of bonds in a compound, which is a key concept in chemistry.

Metallic Character

Metallic character refers to how easily an atom can lose its electrons to form positive ions, a trait commonly associated with metals. As you move down a group in the periodic table, the metallic character typically increases.

This is because atoms get larger and their valence electrons are further from the nucleus, making them less strongly attracted and easier to remove.

• Increased metallic character leads to higher conductivity of heat and electricity.
• It also often relates to greater malleability and ductility.

This trend is why elements become more metallic in nature when moving down a group, and helps explain the nature of chemical reactions for metals compared to nonmetals.

Oxides

Oxides are compounds formed by the reaction of oxygen with another element. The nature of these oxides, whether they're acidic, basic, or amphoteric, depends mainly on the elements they are bonded with and their position in the periodic table.

For instance, down a group in the periodic table, the basicity of metal oxides generally increases. This is tied to the increase in metallic character. Metals further down a group more readily lose electrons and form compounds like basic oxides, which react with acids.

• Nonmetal oxides, for example, are often acidic in nature.
• In contrast, metallic oxides tend to be basic.

Understanding the nature of oxides is important because it gives insight into the reactivity and properties of a substance in chemical reactions.